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LEARN SOLIDITY LESSON 5: Mappings Solidity. Addresses Ethereum. Msg.sender Solidity

LEARN SOLIDITY LESSON

Mappings Solidity. Addresses Ethereum. Msg.sender Solidity


Addresses Ethereum

The Ethereum blockchain is made up of accounts. Each account has an address, which you can think of like a bank account number. It's a unique identifier that points to that account, and it looks like this:

0x0cE446255506E92DF41614C46F1d6df9Cc969169

Mappings Solidity

A mapping is essentially a key-value store for storing and looking up data. In the first example, the key is an address and the value is a uint, and in the second example the key is a uint and the value a string.
mapping (address => uint) favoriteNumber;

function setMyNumber(uint _myNumber) public {
 
  favoriteNumber[msg.sender] = _myNumber;
}

Msg.sender Solidity

In Solidity, there are certain global variables that are available to all functions. One of these is msg.sender, which refers to the address of the person (or smart contract) who called the current function.

mapping (address => uint) favoriteNumber;

function setMyNumber(uint _myNumber) public {
  // Update our `favoriteNumber` mapping to store `_myNumber` under `msg.sender`
  favoriteNumber[msg.sender] = _myNumber;
  // ^ The syntax for storing data in a mapping is just like with arrays
}

function whatIsMyNumber() public view returns (uint) {
  // Retrieve the value stored in the sender's address
  // Will be `0` if the sender hasn't called `setMyNumber` yet
  return favoriteNumber[msg.sender];
}



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